Matt said in his blog last week that he would only use the diamond veto on himself. He feels it will put more suspicion of him being the saboteur, and the brigade might get upset for him keeping it secret. I think he could use it on Regan and tell everyone that he had to keep it a secret and if he told anyone he would lose the power, just like Jeff couldn't say anything last season. At least then everyone wouldn't suspect that he got $$$ for opening Pandora's box.